The work aims to study the effect of 1H-benzotriazole (BTA) in NaCl solution on the galvanic corrosion behavior of carbon steel/copper alloy. The potential distribution, current density distribution and EIS evolution of the WBE in NaCl solution with and without BTA were studied by the wire beam electrode (WBE) and electrochemical impedance spectroscopy (EIS) techniques. Meanwhile, the EIS characteristics of the carbon steel area and the copper alloy area were compared and analyzed. After immersion for 72 h under the condition without BTA, the anodic current area on the carbon steel surface accounted for 80%, and the range of current density distribution was narrow. After immersion for 72 h under the condition with BTA, the proportion of anode area on the surface of carbon steel was 86%, and the range of current density distribution was significantly enlarged. The impedance value of the copper alloy under the condition with corrosion inhibitor was greater than that of the copper alloy under the condition without corrosion inhibitor. However, the impedance value of carbon steel in the solution with and without BTA was relatively small. When copper alloy and carbon steel are electrically coupled in NaCl solution, the electrochemical inhomogeneity of carbon steel is increased due to corrosion inhibition effect of BTA. In the galvanic corrosion process of carbon steel/copper alloy, BTA only plays a good corrosion inhibition effect on the copper alloy, and the corrosion inhibition effect of BTA on carbon steel is not obvious. Compared with the carbon steel/copper alloy couple, when the copper alloy is individually immersed in a solution containing BTA, the Cu-BTA molecular film formed on the surface is more stable and the corrosion inhibition effect is better. With the extension of the immersion time, the electrode reaction rates of the WBE in the NaCl solution added with BTA are gradually increased, while the changes of the electrode reaction rates of the WBE under the conditions without BTA are exactly the opposite.